What symptoms are you having? Alternator output is controlled by the BCM, not internally in the alternator. Voltage will vary from 12 to 15 volts depending upon battery state and demand.

 

Current none but when I do have symptoms it will be headlights dimming like a bad alternator and battery gauge drops below the “safe” bracket. At one point the truck shut off on me while driving bc it was all battery. I’m not sure if it’s a bad ground or a bad wire to the BCM. Side note I’m on alternator 5 bc of this issue

 

Have you had the battery load tested?


Charging a battery from dead, or near dead, is hard on an alternator because of the length of time it needs to run at high output with a break.

 

Have you had the battery load tested?


Charging a battery from dead, or near dead, is hard on an alternator because of the length of time it needs to run at high output with a break.

I took it to the auto parts store and had the battery tested and it was good.

 

Maybe check what the voltage is? Maybe the belt driving it is too loose (tensioner is failing), or has some grease on it so it's slipping.

Edit: changed "that" to "what", for the first sentence to make more sense.

 

Maybe check that the voltage is? Maybe the belt driving it is too loose (tensioner is failing), or has some grease on it so it's slipping.

Well the belt seems nice and tight and is clean. So possibly the tensioner however I’m not sure

 

At least check what voltage is at the battery and at the alternator. Perhaps there's a bad connection/wire somewhere, so the ecu is telling the alternator to put out max power, but the bad connection prevents the electrical system & battery from actually getting that power.

 

I’ll try that to thank you

 

The rvc sensor on our trucks is right by the battery. The negative cables go through it. It’s a ring that the wires go thru and it has a plug on that ring. I’m not sure if the rvc sensor ever goes bad but I guess it could. I have mine unplugged. So my voltage stays at 14 volts all the time instead of the ecu controlling it.

 

Alright Gents my truck was running fine until today. My music was turned down so I was able to hear an electronic click on my a driver side in the truck. Then my voltage dropped. So bad BCM or ground to BCM?

 

Obviously it is a bad bcm.

From that tiny amount of detail you gave us, it is not possible to diagnose what wire and/or part it might be.

 

I see this thread is old, but I’m chasing an issue my truck dead but will have the check engine light lit up, but it has no power to the OBD two ports you cannot turn on the radio dome lights in any bit of electronics is totally shut down. I am replacing the ignition switch in the relay in the morning all my grounds in the battery seem good. My battery was pumping out 15 V which has been giving me some concern. Now Wood anybody on this thread recommend me replacing my BCM the truck sat for numerous months it’s a 2013 GMC Sierra 1500 WT it was owned by the Canadian government so it was looked after well bus it was parked for about six months.

 

The computers in your truck are the least likely things to fail. For pretty much every diagnostic procedure GM writes up for your vehicle, replacing a computer is at or near the end of the procedure, not the first thing to do. Mechanics will suggest it up front, because it's easy to do, cheap for them and highly profitable, and then you are financially invested in fixing the problem, so you are more likely to spend more for them to do electrical testing to find what the actual problem is.

"all my grounds in the battery seem good" is, frankly, a ridiculous statement. There is no "seem". You need to disconnect, clean both sides of the connection, then reconnect all the main power AND ground cables between the battery, engine, frame, cab and fuse box.

Then work on getting the obdii port to get power, like checking the cigarette lighter fuse.

 

yeah man to say that it sounds frankly ridiculous. I think you’re frankly ridiculous to be quite honest. You offered no insight whatsoever. I done everything that you’ve mentioned just because I didn’t use fancy terms and sound like I’m a Silverado or Sierra expert doesn’t mean that I’m not intelligent with vehicles I’m a trained autobody technician that’s pretty good mechanically and I’d appreciate to be treated as such not like a common idiot. I’d appreciate some real insight not somebody telling me to start where I’ve been many times trying my battery is fine. My grounds are fine and doing some research. It seems like it could only be a BCM magnificent switch or relay. I jumped on the thread for some insight not for some idiot to break me down. Enjoy your night


Furthermore, if you understood my problem, you know that that’s an impossible feast to get power to all that stuff. The truck is shutting power off after that and sending a signal deliberately it’s just to decipher the signal as somebody that’s not a dealer.

 

Well, posting that connections "seem good" is the kind of thing people post, who are unfamiliar with how electricity works post. But feel free to ignore my advise on dealing with electrical problems for these trucks, I'm sure your autobody training will serve you well for fixing them.